The unofficial google drive linux CLI supports encryption with custom keys too.
I then went and bought 1TB of Google Drive and now all my photos and anything else is backed up onto both Google Drive and my NAS. It's all encrypted so yeah, should be safe enough. The handy thing about the 1TB Google space is that it's shared amongst all their products, so, I don't need to think about running out of Gmail space either.
Don’t think it allows you to take advantage of delta-byte syncing though because while compression algorithms can now cater for the rsync-like delta sync functionality you find in some cloud storage clients my guess is that wouldn’t be optimal for secure encryption (but I don’t know it’s just a guess) - but if you aren’t changing the files a lot the speed degradation may be outweighed by your desired outcome.
It also works well for Dropbox shared folders in case you have the need to share folders with other people but still want this additional layer of encryption.
And of course since it’s open source it may make you feel more comfortable about the encryption.
Of course it works when you download the file too.
Most of my (not at home) stuff is backed up to a server (that I own) at $work (ISP), though.
I'm still looking for the perfect solution (for me).